share front, insteat of back end link

[Anguandia]

What does this PR do?

Share the front end link to an article as opposed to sharing the back end link

Description of Task to be completed?

• Pass the link to share in the body of the share request

How should this be manually tested?

• Run this backend
• On postman, make a post request to http://localhost:<your port>/api/v1/articles/<valid article slug>/share/<[mail, facebook or twitter>
• Copy any webpage URL and supply it as the url property value in the request body
• Ensure you have a valid token
• Expect a browser window to open for interactive completion of the sharing
• After completing the sharing dialogue, open whichever forum you shared to and click on the received link
• You should see exactly the same page you shared

Any background context you want to provide?

The previous implementation shared the backend link to the article that returned the raw resource from the database, not readable, especially images

What are the relevant pivotal tracker stories?

Fixes #169619406

Screenshots (if appropriate)

Questions: